but another question: where to find a good tutorial about
node, nodeset and this parent:: self:: ancestor:: and so on
i need to understand this stuff.

I drew a diagram on axes that I found very helpful for referencing and I've
given specific permission for it to be used by other training companies as
well when asked. This is on page 57 of the freely downloadable preview of
our book, found from the "Book Sales" link at the top of our home page.